Supplementary lens for viewing a video or computer screen

ABSTRACT

A device ( 5 ) for viewing a display screen ( 2 ), including a large-area visual medium ( 1 ) that can be placed in front of the display screen ( 2 ), characterised in that the visual medium ( 2 ) has a focal length f of at least 615 mm. The visual medium ( 2 ) is preferably a large-area lens ( 1 ) that is optimised for viewing an entire display screen ( 2 ) with both eyes ( 4 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of viewing aids for observing displayscreens. It relates to a device for observing a display screen.

2. Description of the Related Art

Such a device is known for example from the U.S. Pat. No. 6,417,894. Asupplementary lens is described in this, which is fastened to a computerscreen by way of a holding arm and is envisaged for an eye distance of 5cm to 20 cm in front of the lens. By way of this one may achieve anapparent picture distance of infinity, by which means the accommodationof the eyes for presbyopic users is to be simplified. Numerous ergonomicproblems and problems with regard to operating physiology howeverremain.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a device forobserving a display screen which permits improved working conditions anda non-tiring viewing.

This object is achieved by a device for observing a screen.

The invention offers the following advantages:

By way of the fact that the picture appears to the observer in itsentirety and in relatively large manner, its observation leads tocontinuous slight movements of the head which counteracts a stiffeningof the neck and shoulder muscle system.

By way of the fact that an optically effective diameter of the device isrelatively large, a binocular observation of the complete screen ispossible. The pictures appears brighter to the user on account of thefocussing of the light emitted from the screen.

By way of the magnifying effect of the device, the picture distance,i.e. the distance at which the observed object or screen appears to theuser becomes larger. By way of this the burden to his eyes is reduced bythe accommodation. The picture distance may be selected up to infinity,but it has been shown that a certain residual accommodation isadvantageous. At the same time the picture distance should not be closerthan a “minimum of the visual range” of an observer. The smallest clearvisual range for young persons may be up to 25 cm and increases with anincreasing age up to approx. 1 m. Advantageous is a clear visual rangeof 0.5 m to 2 m, corresponding to normal visual behaviour.

Preferably the optical medium has a focal width f between 650 mm and2'000 mm. A large-surfaced lens with an enlargement may be designed in acomparatively thin manner on account of the large focal width.

This selection corresponds to an optimum of size and weight of thevisual medium, in particular of an individual lens with which smalldistances between the observer, lens and screen are possible, even withlarge screens. The screen therefore appears in its complete manner andat a comfortable distance even with restricted spatial conditions, sothat only a low accommodation is required.

Preferably on use of a single lens, its parameters, in particular theradii of curvature of the two sides of the lens are selected such thatastigmatism and coma are low and compensated for both eyes over thecomplete picture. Simultaneously, by way of a suitable selection of thefocal width in combination with the distance of the object and distanceof the eye, the picture warping or distortion is minimised. This type ofparameterisation of the lens differs from the conventional procedure:Conventionally, a lens or a lens system is optimised for an observationpoint on the optical axis or lens axis. This is correct for one half ofa binocular glass or for a magnifying glass used with one eye. Binocularvision through a large lens however sets different demands. Conventionallenses or magnifying glasses with the use with both eyes demand aprecise arrangement of the lens, eyes and the object, and even then onlyhave a small usable region in which chromatic distortion and picturedistortion are acceptable.

The type of parameterisation according to the invention is effected byway of simulation of the imaging of object points onto perceived picturepoints. At the same time one assumes a perception by the eyes which lieoutside the lens axis, and the imaging is carried out for differentcolour components of an object point. The object points are blurred,i.e. are imaged onto different picture points, in particular on accountof the coma effect and the chromatic aberration of the lens. The picturethus becomes slightly blurred. The parameterisation according to theinvention is deduced by a systematic variation of the lens parametersuntil a uniform distribution of the fuzziness onto the whole pictureresults.

Preferred parameters of an individual lens which result from thisoptimisation are: focal width between 1000 mm and 1200 mm, eye distanceto the lens between 300 mm and 600 mm, and distance of the object to thelens between 300 mm and 500 mm. For a biconvex lens, a radius of aninner lens surface is preferably between 300 mm to 1'000 mm, inparticular between 450 mm and 700 mm, and a radius of an outer lenssurface preferably between −600 mm and −10'000 mm, in particular between−1'200 mm and −10'000 mm. For a concave-convex lens, a radius of theinner lens surface is preferably between 300 m to 1'000 mm, inparticular between 450 mm and 700 mm, and a radius of the outer concavelens surface is preferably between 1'000 mm and 10'000 mm, in particularbetween 4'000 mm and 6'000 mm.

With an embodiment optimised in such a manner, the further advantage ofthe invention results: individual picture points of a tube or LCD screenare not enlarged in an ideal manner, but slightly blur into one another.The impression of pixels disappears. This smoothing of the picture verysurprisingly is subjectively perceived to be quite pleasant. An idealenlargement of the screen would also enlarge the picture points andrender these better recognisable. Although this is good news for thetheoretician, it is however annoying for the observer since he is notinterested in the individual picture points, but in the total picture.

The lens is advantageously manufactured of plastic, in particular ofPMMA (poymethylmethacrylate) or of CR39. CR39 is usually used formanufacturing plastic lenses of spectacles.

In a further preferred embodiment of the invention, the visual mediumcomprises a system of several lenses. These are preferably connected toone another with a positive fit.

Further preferred embodiments are to be deduced from the dependentpatent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter the subject-mater of the invention is described in moredetail by way of preferred embodiment examples which are represented inthe accompanying drawings. There are shown in:

FIG. 1 a schematic representation of a beam path in an optical system;

FIG. 2 a schematic representation of a beam path in an optical systemaccording to the invention;

FIG. 3 a view of a first embodiment form of a device according to theinvention; and

FIG. 4 a plan view of a second embodiment form of a device according tothe invention.

The reference numerals which are used in the drawings and theirsignificance are listed in the list of reference numerals. Basically thesame parts are provided with the same reference numerals in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1, for explaining the optical basics, shows a schematicrepresentation of a beam path in an optical system. A lens 1, an object2 and an eye 4 of an observer are shown in a dashed manner seriallyalong a lens axis 6 or optical axis. An eye distance a is equal to thedistance of the eye 4 to the lens 1, or put more accurately, from thelens middle which is usefully defined, and an object distance g is equalto a distance of the object 2 to the lens l. A part of the object 2 isshown represented as a bold arrow. Without the lens it would appear tothe observer at an angle α and at a distance a+g. By way of the effectof the lens l it appears enlarged to the observer as a virtual picture 3at an angle 1 and at a distance a+b, wherein b is the picture distanceto the lens l. The imaging is summarised by the equation,$\frac{1}{f} = {\frac{1}{b} - \frac{1}{g}}$wherein f is the focal width of the lens l and the object distance g byconvention has a negative sign. A size ratio of the picture 3 to theobject 2 is indicated as the theoretical enlargement vt. Thus thefollowing appliesvt=b/g=f/(f+g)

The eye 4 sees the object 2 through the lens l at the larger angle 1than without the lens l at the angle α. A visualised enlargement vs isaccordingly defined by an angular ratio${vs} = {{{\tan(\alpha)}/{\tan(\beta)}} = {\frac{b\left( {g + a} \right)}{g\left( {b + a} \right)}.}}$

With a positive lens the visualised enlargement vs is smaller than thetheoretical enlargement vt.

If one relates the picture distance b and the object distance g to thefocal width f, then one obtains related variablesc=g/f and e=a/f

with which the visualised enlargement vs may be expressed as${vs} = {\frac{c + e}{c + e + {eg}}.}$

If the dependence of vs is plotted for values of c and e in each casebetween 0 and 1, then it is evident that the visualised enlargement vsachieves its greatest increase for values of c and e in each case ofsmaller than 0.5. In particular the enlargement vs increases for valuesof e between 0 and 0.5, and for values between 0.5 and 1 only in acomparatively weak manner. An increasing eye distance a then onlyentails a weak increase in the enlargement. Since with a computer screenthe eye distance a is advantageously selected larger than the objectdistance g or the screen distance, preferably values of c between 0.2and 0.6 and values of e between 0.3 and 0.7 are selected. These permit afocal width f of 0.8 m to 2 m.

FIG. 2 shows a schematic representation of a beam path in an opticalsystem according to the invention. For the purpose of a better overview,the object 2 and the picture 3 have not been drawn in as a whole, butonly the respective representative arrows. A beam path between an object21 at the end of the arrow tip in the plane of the object 2 and an eye 4is drawn in schematically. Both eyes 4 simultaneously observe the objectpoint 21 through the large-surfaced lens l and see it as a picture point31. The eyes 4 in each case are distanced to the lens axis 6 by half theeye middle distance ya.

In contrast to conventional theory, the lens is not optimised for anindividual eye on the lens axis 6 but for two distanced eyes 4. Arespective perceived picture point 31 is determined proceeding from anobject point 21, and specifically for various spectral components of thelight emitted from the object point 21. For this, proceeding from aknown position of the object point 21 and of the observed eye 4 and alens arrangement and geometry which is assumed as being given, aboundary value problem is solved in order to determine the beam pathfrom the object point 21 to the eye 4. The law of refraction at the sametime must be fulfilled on the surfaces of the lens 1, thus on an innerlens surface 11 and on an outer lens surface 12.

The entry angle ε1 and the exit angle ε2 of a beam corresponding to thedefined beam path are exterior angles. The following appliesε1=φ1+ψ1 and =φ2+ψ2

The light beam experiences the smallest deflection and thus also thesmallest error if the entry angle ε1 and the exit angle ε2 are equal toone another. This requirement may however not be fulfilled over thecomplete picture region for a large-surfaced lens and an extendedobject. The eye 4 perceives a bundle of light beams which is emitted bythe object point 21 as coming from the picture point 31. The apertureangle of this bundle is relatively small due to the small opening of thepupil. The bundle is not imaged onto the picture point 31 in an accuratemanner due to astigmatism and coma. Astigmatism relates to beam bundleswhich pass the lens 1 in a slanted manner and coma concerns widelyopened beam bundles. Chromatic errors lead to the fact that the bundle,depending on the colour, or spectral components of the bundle are notperceived in the picture point 31 in an exact manner. For example agreen, a red and a blue object point 21 which overlap in the plane ofthe object, thus lie at the same location, do not lie at the samelocation in the picture plane; thus they are perceived lying atdifferent locations. Chromatic errors may not be corrected with anindividual lens which is why a material with a small dispersion, forexample PMMA is used.

A white object point 21 is thus perceived as a blurred or distortedpicture point 31. An optimum is found in the following manner so thatthe blur is distributed uniformly: This blur or distortion of thepicture point 31 is determined for several, for example 28 object points21 which are distributed uniformly over a quadrant of the completesurface or of the plane of the object 2. The imaging for example in eachcase of eight blue, green and red beam bundles is determined for eachpoint. The average square of the errors of the deviations are summed asa measure of the deviation for each point. For optimisation, the errorsare summed over all the points and for both eyes, thus in total for 56points. Additionally the blur is empirically evaluated. For a givenfocal width f the radius r1 of the inner lens surface 11 and the radiusr2 of the outer lens surface 12 are systematically varied until as anoptimum, a uniform and as a whole minimal distribution of the blur overall observed object points 21, thus over the entire picture and for botheyes 4 is found. The lens 1 is optimised for the observation of theentire object 2 with both eyes 4 by way of this. This variation of theradii may be repeated for other focal widths f and respective objectdistances g and picture distances b as the case may be.

Preferably the radius r1 of the inner lens surface 11 is smaller thanthe radius r2 of the outer lens surface 12. By way of this, thedistortions are smaller than in the reverse case.

Conventional methods for the design of a lens however provide optimalimaging for only one eye on the lens axis 6. One also optimises for arelatively large bundle of light beams which emanate from the objectpoint 21. A curvature of the lens 1 or radii r1 and r2 are determinedwhich are different than according to the method described above. Forthis reason, the various blurs and distortions increase with anincreasing eye middle distance ya to the lens axis 6, so that only asmall part of the field of view is seen in an adequately well-definedmanner and may indeed be used. The blurred regions lead to an irritationof the observer and strenuous movements on attempting to see a certainregion of the picture in a well-defined manner.

The use of the above-described optimisation method according to theinvention for example yields the following preferred values for anaverage eye middle distance ya of 68 mm (all measures in millimetres):object distance g eye distance a r1 r2 focal width f = 1200 mm −300 300529.5   5′000 −300 450 558.4 −10′000  −300 600 770.0 −2′500 −450 300529.5   5′000 −450 450 627.1 −10′000  −450 600 833.7 −2′000 focal widthf = 1000 mm −300 300 449.4   5′000 −300 450 586.2 −3′000 −300 600 726.0−1′500 −450 300 517.0 −10′000  −450 450 609.6 −2′500 −450 600 783.9−1′300

Negative values of r2 correspond to a biconvex lens, positive values ofr2 to a concave-convex lens. Values of the radii which are approximatelyequal to the specified values are preferred. A variation of the radii ofaprox. 10% to 20% about the specified values still lead to good results.Also instead of lenses with a large r2, for example −10'000 mm, one mayalso use piano-convex lenses.

The focal width f is preferably at least approx. 600, 650 or 700 mm sothat a greater enlargement is possible without distortions which wouldoccur at small focal widths f becoming too large. On the other hand thefocal width f is preferably 2000 mm at the most, since for larger valueswith a meaningful object distance g, the resulting enlargement would notbe sufficient. Thus preferred focal widths lie in the range of 800 mm to1500 mm.

The object distance g is preferably between 160 mm and 1500 mm, inparticular between 200 mm and 800 mm. Smaller values of up to forexample 30 mm are also possible, but with a correspondingly smalleramplification. The eye distance a is preferably 100 mm to 1500 mm, inparticular 205 mm to 1400 mm.

The diameter of the lens l is preferably larger than 250 mm, inparticular it is larger or equal to 380 mm and smaller than 1000 mm.

In a preferred embodiment of the invention, the lens is plano-convex,with a diameter of approx. 380 mm and a radius of curvature of theconvex side between 550 mm and 640 mm, in particular 585 mm and 605 mm,and preferably at least approximately 594 mm.

The lenses according to the described embodiments of the invention arepreferably antireflected on one or both sides. The antireflection iseffected by way of depositing one or more optically active layers in avapour deposition or immersion method or by way of sticking on anantireflecting film or an antireflecting laminate.

Since a laminate with a thickness for example of approx. 0.2 mm as arule is constructed of several layers and is harder and stiffer incomparison to a film, thus may not be greatly stretched, the laminate ispreferably stuck onto the plane side of a plano-convex lens.

FIG. 3 shows a front view of a first embodiment of an observation device5 according to the invention. It comprises a round lens l with adiameter of 380 mm, consists of the material PMMA(polymethylmethacrylate), and has a weight of about 1.3 kg. In thisexample, the lens is biconvex and for minimising the imaging errorscomprises two different radii of curvature. The observation device 5comprises an adjustable holding arm 53 for positioning the lens 1 infront of a screen, in particular a computer screen. The holding arm 53may be fastened to a table and preferably has five or six degrees offreedom in which the lens l may be moved. The lens l may also bedesigned in an oval or rectangular or square manner.

FIG. 4 shows a front view of a second embodiment of an observationdevice 5 according to the invention. The applied lens l is rectangular,wherein a diagonal of the rectangle is essentially equal to the lensdiameter of the previous embodiments. The lens l is fastened to a foot51 via an optional inclining or setting device 52 and this foot may beplaced onto the surface of a table. The foot 51 for example comprisesexchangeable elements for achieving different heights of the lens labove the surface of the table. In a further embodiment of theinvention, the foot is formed in a bridge-like manner so that it may beplaced over a computer keyboard, which permits a larger object distanceg. Of course such a foot may also be combined with a round or adifferently shaped lens 1.

LIST OF REFERENCE NUMERALS

-   f focal width-   g object distance-   b picture distance-   a eye distance-   l visual medium, lens-   11 inner lens surface-   12 outer lens surface-   2 object-   21 object point-   3 picture-   31 picture point-   4 eye-   5 observation device-   51 foot-   52 adjustment means-   53 holding arm-   54 table-   6 lens axis.

1. A device for observing a display screen (2), comprising alarge-surfaced visual medium (1) which may be arranged in front of thedisplay screen (2), characterised in that the visual medium (1) has afocal width (f) of at least 615 mm.
 2. A device according to claim 1,characterised in that the device is optimised for observing a completedisplay screen (2) with both eyes (4).
 3. A device according to claim 1,characterised in that the device is envisaged for an eye distance (a) ofmore than 220 mm.
 4. A device according to claim 2, characterised inthat the device is envisaged for an eye distance (a) of 220 mm to 1500mm.
 5. A device according to claim 1, characterised in that the deviceis envisaged for an object distance (g) of 100 mm to 1500 mm.
 6. Adevice according to claim 1, characterised in that the visual medium hasa focal width (f) of 620 mm to 2000 mm.
 7. A device according to claim1, characterised in that the visual medium has a focal width (f) of morethan 800 mm.
 8. A device according to claim 1, characterised in that thedevice has a diameter of 250 mm to 1000 mm.
 9. A device according toclaim 1, characterised in that the device has a diameter of more than370 mm.
 10. A device according to claim 1, characterised in that thedevice comprises a system of several lenses.
 11. A device according toclaim 1, characterised in that the device comprises a single lens (l).12. A device according to claim 11, characterised in that the lens (l)is plano-convex, concave-convex or biconvex.
 13. A device according toclaim 12, characterised in that the lens (l) is biconvex and has a firstradius of curvature (r1) in the region of 300 mm to 1,000 mm and asecond radius of curvature (r2) in the region of −600 mm to −10,000 mm.14. A device according to claim 12, characterised in that the lens (l)is concave-convex and comprises a first radius of curvature (r1) in theregion of 300 mm to 1,000 mm and a second radius of curvature (r2) inthe region of 1,000 mm to 10,000 mm.
 15. A device according to claim 12,characterised in that the lens (l) is piano-convex, and has a radius ofcurvature in the region between 550 mm and 660 mm, preferably between585 mm and 605 mm.
 16. A device according to claim 11, characterised inthat the lens is antireflected at least on one side by way of a filmwhich is stuck on, or a laminate.
 17. A device according to claim 11,characterised in that the lens is antireflected at least on one side byway of one or more optically active layers which are vapour deposited ordeposited by an immersion method.
 18. A device according to claim 1,comprising a holding means (53; 51,52) for arranging the visual medium(1) in front of the display screen (2).
 19. A device according to claim18, wherein the holding means is an adjustable arm (53) with severaldegrees of freedom which may be fastened on a table (54).
 20. A deviceaccording to claim 18, wherein the holding means is a table stand (51)with means (52) for adjusting the height and/or inclination of thevisual medium (1).